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Detailed Look at Molecular Railway Ties

WASHINGTON, D.C.--Biophysicists have solved the structure of a protein that makes up the cell's internal rail system, transporting everything from proteins to DNA. The new structure, unveiled here last week at a meeting of the American Society for Cell Biology, may help researchers design better anticancer drugs and fungicides.

The protein, called tubulin, aligns into long tubular filaments that shuttle molecules through the cell and are essential for guiding chromosomes during the line dance of cell division. For years, attempts to use x-ray crystallography to determine tubulin's structure failed because the protein refused to crystallize properly.

Taking another tack, Kenneth Downing and Eva Nogales of the Lawrence Berkeley National Laboratory in California crafted a tubulin sheet just one molecule thick--a simpler task that allowed them to use an alternative technique called electron beam crystallography. They bounced very low energy electrons off the sheet from many different angles to compose a three-dimensional image. The tubulin structure will appear in the 8 January 1998 issue of Nature.

"It's a huge milestone in the cytoskeleton field," says Duke cell biologist Harold Erickson. The structure reveals how tubulin's two parts interlock and which amino acids appear to be crucial for the protein to latch onto other molecules. The structure also shows the binding site of taxol, an important anticancer drug that works by tossing up roadblocks on the microtubule highway. That information might allow researchers to design a family of microtubule disrupters.